The invention relates to a rheometer or rheometer attachment which is used to measure the viscosity and stress relaxation of polymers, elastomers, and rubber compounds in simple extension.
Joachim Meissner, in the review article xe2x80x9cPolymer Melt Elongation-Methods, Results, and Recent Developmentsxe2x80x9d in Polymer Engineering and Science, April 1987, Vol. 27, No. 8, pp. 537-546 describes different extensional rheometers that have been developed in the prior art. Meissner is also the author of several patents on the subject including U.S. Pat. No. 3,640,127, dated Feb. 8, 1972, German 2138504, dated Aug. 2, 1971, German 2243816, dated Sep. 7, 1972 and U.K. 1287367.
Extensional rheometer designs by Cogswell, Vinogradov, and later Mxc3xcnstedt had in common that one end of the polymer fiber or filament that was used for testing was fixed to a load cell/indicator, while the other end was stretched by mechanical means to a finite maximum elongation. Accordingly, these rheometers operated with a non-uniform extensional rate throughout the sample particularly near the clamped ends of the fiber. Meissner overcame these difficulties with his dual rotary clamp design in which rotary clamps stretched the fiber at either end over a fixed gauged length. See, for example, xe2x80x9cRotary Clamp and Uniaxial and Biaxial Extensional Rheometry of Polymer Meltsxe2x80x9d by J. Meissner, et al., Journal of Rheology, Vol. 25, pp. 1-28 (1981) and xe2x80x9cDevelopment of a Universal Extensional Rheometer for the Uniaxial Extension of Polymer Meltsxe2x80x9d, by J Meissner, Transactions of the Society of Rheology, Vol. 16, No. 3, pp. 405-420 (1972). In a further development of this type of rheometer, in order to improve the transfer of the circumferential speed of the clamps to the local speed of the sample at the location of clamping (strain rate lag), two rotary clamps in the prior art devices were replaced by Meissner and Hostettler as illustrated in xe2x80x9cA New Elongational Rheometer for Polymer Melts and other Highly Viscoelastic Liquidsxe2x80x9d, Rheological Acta, Vol. 33, pp. 1-21 (1994) with matched/grooved, metal conveyor belts. With this design, however, a measurement was limited to a single rotation of the clamps corresponding to a Hencky strain of seven, and the maximum extensional rate was limited to 1/s (a reciprocal second). The extensional viscosity was determined from the force required to deform the fiber, which was measured by the deflection of leaf springs supporting one set of rotating clamps.
Other techniques used to measure extensional viscosity involved winding one end of a fiber around a drum and measuring the resultant stretching force at the other fixed end of the fiber, as illustrated in U.S. Pat. No. 3,693,425 (1972) by J M Starita et al. Like the earlier designs, this method imparted a non-uniform extensional deformation to the free gauge length of the stretched fiber, particularly at the fixed end of the fiber. Further, the windup was uncontrolled and precautions had to be taken to ensure that windup did not take place over a portion of previously wound fiber.
An apparatus for measuring the rate of extensional flow of low modulus solids comprises; (a) a drive shaft mounted in an armature, the armature being connected to a torque shaft, and (b) two rotatable drums in proximity to one another, wherein a first drum is mounted in the armature substantially in alignment with the torque and drive shafts, and a second drum is adjacent thereto.
In the illustrated embodiment, the first and second drums are in substantially parallel alignment, are mounted on bearings, and may have associated therewith means for directing the windup of a sample on the drums. The drums may be geared to be counter rotating or co-rotating. In the illustrated embodiment, the drums are geared such that the drums rotate at the same speed.
Also provided is a method for measuring the rate of flow of low modulus solids comprising the steps of, a) providing an apparatus for measuring the rate of extensional flow of low modulus solids comprising a drive shaft mounted in an armature wherein the armature is further connected to a torque shaft, two rotatable drums in proximity to one another wherein the first drum is mounted in the armature substantially in alignment with the torque and drive shafts and the second drum is adjacent thereto, b) fixing a sample to both drums, one end of said sample being attached to each drum, c) causing the two ends of the sample to be pulled away from each other by rotation of the drums, and d) measuring the torque created in the torque shaft by the drawing of the sample.
The method may further comprise the steps of measuring the maximum torque achieved by the sample and measuring the lapsed time from the start of the measurement to the breaking of the sample. In the illustrated embodiment of the method, the two rotatable drums are mounted substantially in parallel alignment on bearings, and the drums have associated therewith means for directing the windup of a sample on the drums.
The dual windup threaded drum extensional rheometer illustrated, makes possible the windup of each end of a fiber and imparts a uniform extensional deformation to the unsupported pre gauge length of the fiber, and allows for large extensional deformations by allowing multiple drum rotations with a threaded drum design.
The rheometer provides a simple design and method to measure the extensional flow properties of polymers, elastomers and compounds. The rheometer of the invention can be attached to any commercially available rotational rheometer, and can be made small enough to fit within the environmental chamber of a rotational rheometer in order to measure extensional flow properties as a function of temperature. The invention may also be part of, or be incorporated into a new type of rheometer. The apparatus can also be used to measure the extensional properties of viscoelastic solids.